My tandem has two small screws above each bottom bracket, one on each side (so four in total). I've not seen them on any other bike, and I can't figure out what they're for! Suggestions so far have been (a) letting water out (except that they're on the top) and (b) putting oil in (except that I didn't think that was how you're meant to service a bottom bracket - I thought you had to take it apart). I know they're not for an eccentric bracket, as there's other screws elsewhere for that. Picture of screws on rear bracket here: http://s8.postimage.org/z4evs6791/IMG_1950.jpg

This is a nice bike. Could you post MORE (and sharper) photos of it, here or elsewhere?
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heltonbikerSep 28 '12 at 5:25

@heltonbiker Unfortunately it's more accurate to say it was a nice bike - the years and the previous owners have taken their toll somewhat. And I'm pretty sure that the guy I bought it from on ebay ("I was going to do it up for the kids, but didn't get round to it") has re-installed the spindles the wrong way round (it's just about visible in the photos). I'm planning to take some photos and post them - in the meantime, it looks a bit like this but worse.
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evsmithOct 1 '12 at 0:31

force-feeding grease with guns through those nipples looks like something common long time ago, I have already seen it in many types of machinery from the past (when things were intended to last and be serviced many times). The principle is to remove the old grease with new one, or something like that. No wonder they gave up doing this, but apparently it was "the way to go" at the time...
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heltonbikerSep 28 '12 at 5:23

Grease zerks are not "from the past". While most automotive bearings are now sealed for "life", lots of heavy equipment, manufacturing equipment, etc, still uses zerks. And the idea of removing the old grease with the new works -- if you'd ever seen it done you'd understand this.
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Daniel R HicksSep 28 '12 at 11:49

1

Yeah, I once worked at a place that had a lawn tractor/front loader and it had plenty of grease nipples on it. You don't see these on bikes anymore because we have sealed bottom brackets. Before sealed hubs you had to take the bottom bracket out to regrease it. With the grease nipples you could regrease without disassembling the bottom bracket.
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KibbeeSep 28 '12 at 12:32

Oops, I did of course mean 'eccentric' - I blame posting too late at night! I've corrected it in the question.
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evsmithSep 30 '12 at 11:36

Grease fittings are still to be found on the Big Toys, but just about everything consumer-focused is of a sealed bearing design. @heltonbiker is right... the old stuff is just forced out by the new stuff.

What you've got there is the same head design for a fitting that's show in the Wikipedia article too. Your crank isn't the sealed type and probably could use some new grease at least once a decade.